Abstract
Vertical splitting cracks often appear in side walls of large-scale underground caverns during excavations owing to the brittle characteristics of surrounding rock mass, especially under the conditions of high in situ stress and great overburden depth. This phenomenon greatly affects the integral safety and stability of the underground caverns. In this paper, a transverse isotropic constitutive model and a splitting failure criterion are simultaneously proposed and secondly programmed in FLAC3D to numerically simulate the integral stability of the underground caverns during excavations in Dagangshan hydropower station in Sichuan province, China. Meanwhile, an in situ monitoring study on the displacement of the key points of the underground caverns has also been carried out, and the monitoring results are compared with the numerical results. From the comparative analysis, it can be concluded that the depths of splitting relaxation area obtained by numerical simulation are almost consistent with the actual in situ monitoring values, as well as the trend of the displacement curves, which shows that the transverse isotropic constitutive model combining with the splitting failure criterion is appropriate for investigating the splitting failure in side walls of large-scale underground caverns and it will be a helpful guidance of predicting the depths of splitting relaxation area in surrounding rock mass.
Highlights
In recent years, the developments of large-scale underground caverns in hydropower stations are dramatically increasing in China
The comparative analysis between numerical simulation and in situ monitoring show that the transverse isotropic constitutive model combining with the splitting failure criterion is appropriate for investigating the splitting failure in side walls of large-scale underground caverns and it will be a helpful guidance of predicting the depths of splitting relaxation area in surrounding rock mass
According the comparison of the numerical results, the displacement curves of the key points are relatively flat when only the Mohr–Coulomb model is employed in numerical simulation, and the calculated results of the key points that near the downstream sidewall of the main power house is far less than the monitoring values, approximately 30 % of the later ones, indicating that cavern deformation caused by the splitting failure exists in the rock masses of the downstream sidewall of the main power house, which can be concluded the isotopic Mohr–Coulomb model is inappropriate for numerical modelling in splitting failures of rock mass
Summary
The developments of large-scale underground caverns in hydropower stations are dramatically increasing in China. The comparative analysis between numerical simulation and in situ monitoring show that the transverse isotropic constitutive model combining with the splitting failure criterion is appropriate for investigating the splitting failure in side walls of large-scale underground caverns and it will be a helpful guidance of predicting the depths of splitting relaxation area in surrounding rock mass. As the load continues to increase, with the effect of free boundary conditions and the interactions among the cracks, the crack propagation will not be stable At this stage, the cracks growth will break out and large-scale splitting cracks will be formed as shown in the Fig. 1c. The rock masses in splitting areas could be simplified to laminated model where the joint plane is perpendicular to the horizontal plane This could be described by the transverse isotropic constitutive models (Jia et al 2008).
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